1. Field of the Invention
The present invention relates to a thermal recording apparatus utilizable in a printer, a digital copier and a facsimile machine for recording imagewise information such as, for example, one or a combination of images and alpha-numeric characters on a recording sheet.
2. Description of the Prior Art
As a thermal recording system in a printer, a thermal transfer recording system is now popularized in which a thermal head is employed in combination with an ink sheet. This thermal transfer recording system is disclosed in, for example, the Japanese Patent Publications No. 62-47717 and No. 63-50198. According to the well-known thermal transfer recording system, the thermal head including a row of heating elements is driven to contact the recording sheet with the ink sheet intervening therebetween. The instant the thermal head is so driven, some of the heating elements in the thermal recording head are selectively energized in response to an electric image signal to melt an ink layer on the ink sheet for deposit on the recording sheet in conformity with the image information carried by the electric image signal.
The thermal transfer recording system has however a problem in that inking material thermally detached from the ink sheet does not satisfactorily deposit on a recording sheet having surface irregularities. Specifically, when it comes to the thermal transfer color recording system such as disclosed in the Japanese Patent Publication No. 63-50198 wherein inking media of three primary colors are deposited in an overlapped relation to give a desired color in the image printed on the recording sheet, the quality of the color image finally printed on the recording sheet tends to be reduced since the deposition of one of the inking media on the recording sheet results in a surface roughening of the recording sheet and, therefore, hampers a satisfactory deposition of the next succeeding one of the inking media on the same recording sheet. This known color recording system has an additional problem in that the recording sheet once deposited with the inking medium of one color at a recording station is apt to be displaced from the recording station when it is repositioned for a deposition of the inking medium of the different color, resulting in an insufficient color reproduction.
The Japanese Patent Publication No. 59-16932 and the Japanese Laid-open Patent Publication No. 62-248669 disclose the recording of image information on not only recording sheets of good surface quality, but also those of low surface quality. According to these publications, the ink image is formed on an intermediate transfer medium and is subsequently transferred from the intermediate medium onto a recording sheet. However, since the inking material deposited on the intermediate transfer medium does not completely detach from the intermediate transfer medium at the time of transfer thereof onto the recording sheet, ink remains on the intermediate transfer medium, and the use of a specially designed cleaning unit is therefore required for removing the ink remains from the intermediate transfer medium.
Also, according to any one of the Japanese Patent Publication No. 59-16932 and the Japanese Laid-open Patent Publication No. 62-248669, the intermediate transfer medium is required to be heated selectively to a temperature when brought to a recording station and also to a different temperature when brought to a transfer station.
To accomplish the selective heating of the intermediate transfer medium to one of the different temperatures, the use is necessitated of a cooling unit in combination with a heating unit, making the recording apparatus as a whole bulky and expensive and also reducing the efficiency of energy use.